In a direct current to direct current power conversion circuit, a bridge circuit is a common application circuit, and the bridge circuit includes a full bridge circuit and a half bridge circuit. The bridge circuit periodically works under control of an inceptive impulse clock timing, and each period is divided into the first half period and the second half period. A power switch in the bridge circuit is classified into two groups: a power switch that is switched on at a first time and a power switch that is switched on at a second time, and the two groups of power switches are switched on in different half periods.
As shown in FIG. 1, a typical full bridge circuit includes a first power switch, a second power switch, a third power switch, a fourth power switch, a transformer K1, a DC blocking capacitor C1, a first synchronous rectifier, a second synchronous rectifier, a sampling resistor R1, a filter inductor T1, and a load. A specific connection relationship is shown in FIG. 1. In the first half period of a period, the first power switch and the fourth power switch are switched on, and the second power switch and the third power switch are switched off. In the second half period of the period, the first power switch and the fourth power switch are switched off, and the second power switch and the third power switch are switched on. The first power switch and the fourth power switch are power switches that are switched on at the first time in the full bridge circuit, and the second power switch and the third power switch are power switches that are switched on at the second time in the full bridge circuit.
As shown in FIG. 2, a typical half bridge circuit includes a fifth power switch, a sixth power switch, a transformer K2, a DC blocking capacitor C2, a first synchronous rectifier, a second synchronous rectifier, a sampling resistor R1, a filter inductor T1, and a load. A specific connection relationship is shown in FIG. 2. In the first half period of a period, the fifth power switch is switched on, and the sixth power switch is switched off. In the second half period of the period, the fifth power switch is switched off, and the sixth power switch is switched on. The fifth power switch is a power switch that is switched on at the first time in the half bridge circuit, and the sixth power switch is a power switch that is switched on at the second time in the half bridge circuit.
For a bridge circuit, to maintain magnetic balance of a transformer, a DC blocking capacitor (such as the C1 in FIG. 1 and the C2 in FIG. 2) is generally connected in series on a primary side of the transformer, and a switch-on time duration of a power switch that is switched on at the first time and a switch-on time duration of a power switch that is switched on at the second time are controlled to be equal in each period, so that a charging time duration and a discharging time duration of the DC blocking capacitor connected in series on the primary side of the transformer are equal, thereby implementing magnetic balance of the transformer. However, when an overcurrent occurs in the bridge circuit, to implement magnetic balance of the transformer, the following technical solutions are generally used.
In the prior art, in a current period, when an overcurrent signal occurs within a switch-on time duration of a power switch that is switched on at the first time, an active level that controls the power switch that is switched on at the first time to a switch-on state is adjusted to an inactive level according to time of occurrence of the overcurrent signal; when no overcurrent signal occurs within a switch-on time duration of a power switch that is switched on at the second time, or when an overcurrent signal also occurs within the switch-on time duration of the power switch that is switched on at the second time, relative to start time of a switch-on time duration of a power switch, if time of occurrence of the overcurrent signal occurring at the second time is later than the time of occurrence of the overcurrent signal occurring at the first time, an active level that controls the power switch that is switched on at the second time to a switch-on state is also adjusted to an inactive level according to the time of occurrence of the overcurrent signal occurring at the first time, so that when an overcurrent signal occurs, it may be ensured that in the current period, the switch-on time duration of the power switch that is switched on at the first time is equal to the switch-on time duration of the power switch that is switched on at the second time, thereby implementing magnetic balance of a transformer. The active level is used to control a power switch to a switch-on state, and the inactive level is used to control the power switch to a switch-off state. For example, the active level may be at a high level, and the inactive level may be at a low level, which depends on a type of a transistor in the power switch and a specific circuit design of the power switch.
However, in the foregoing implementation process, if no overcurrent signal occurs within the switch-on time duration of the power switch that is switched on at the first time in the current period, but an overcurrent signal occurs within the switch-on time duration of the power switch that is switched on at the second time, to ensure that a bridge circuit is not damaged, only the active level that controls the power switch that is switched on at the second time to a switch-on state and is in the current period is disabled according to time of occurrence of the overcurrent signal, but a subsequent signal is not processed according to the current overcurrent signal, which finally causes duration of the disabled active level of the power switch that is switched on at the second time in the current period to be different from duration of the active level of the power switch that is switched on at the first time in the current period. In addition, the subsequent signal is not further processed subsequently; therefore, magnetic balance of the transformer cannot be ensured, thereby reducing reliability of the bridge circuit.